With today's increasing recognition of sustainable global environmental protection, industrial or transportation systems consuming less fossil fuels than conventional or current systems are being actively developed. Examples of such environmentally friendly systems or products are wind turbine generator systems, railroad systems, hybrid cars, electric vehicles and energy efficient air conditioners.
One of the most important devices used in such environmentally friendly systems or products is a high-efficiency rotary electric machine (such as a motor and a generator). In order to manufacture such high-efficiency rotary electric machines, magnets containing rare earth elements (known as rare earth magnets) are widely used. For example, rare earth magnets used in rotary electric machines as drive motors for hybrid vehicles and in rotary electric machines as compressors for air conditioners are required to have a high coercive force even in a high-temperature environment (e.g., approx. 150° C.). Rare earth magnets achieving such a high coercive force contains expensive heavy rare earth elements (such as dysprosium) besides neodymium, iron and boron. Thus, rare earth magnets are now vital for state-of-the-art systems and are expected to have growing demand in the future.
Unfortunately, it is very difficult to recycle (extract and concentrate) a particular rare earth element at low cost. Accordingly, techniques of reducing the use of such rare earth elements while maintaining magnet performance or developments of alternative materials are being urgently studied. However, such techniques are still far from realization. Therefore, immediately important are recycling techniques for extracting rare earth elements from rare earth magnet scraps (such as wasted motors and magnet sludge (cutting scrap) generated during magnet manufacture), and separating and recovering them.
For example, Patent Literature 1 discloses a method for separating rare earth elements, the method including: forming a rare earth halide mixture of divalent rare earth halides and trivalent rare earth halides by halogenating several rare earth elements and/or rare earth compounds in a mixture material, wherein the average valence of two or more rare earth halides in the rare earth halide mixture is from 2 to 3 and the rare earth halide mixture is in a state not dissolved in water or an organic solvent; and then separating the rare earth elements in the rare earth halide mixture into at least two groups by utilizing a property difference between the divalent rare earth halides and the trivalent rare earth halides. According to Patent Literature 1, the separation (ratio) between rare earth elements can be significantly increased compared to conventional methods. Also, when rare earth elements are separated from rare earth concentrates (such as rare earth phosphates), the conventionally essential processing steps (such as acid dissolution, filtration, precipitation removal of impurity, concentration, neutralization and drying) can be spared. Therefore, the separation cost can be considerably reduced.
Patent Literature 2 discloses a method for recovering rare earth elements from a magnet material containing rare earth elements and iron group elements (such as a magnet scrap and magnet sludge), the method including: bringing the magnet material into contact with a gaseous or molten iron chloride; chlorinating only the rare earth elements while not chlorinating the iron group elements; and selectively recovering the rare earth chlorides. According to Patent Literature 2, a lower cost recycle method is provided in which high purity rare earth elements can be extracted from a material (in particular rare earth magnet scraps or sludge) containing rare earth elements and iron group elements and separated from each other.